Bicruciate retaining baseplates are known and have been in use since at least the early 1970s. Their use allows the preservation of both cruciate ligaments, the anterior cruciate ligament (ACL) and the posterior cruciate ligament (PCL). Early designs were predominantly bicompartmental, i.e., the articular cartilage of the distal femur and the proximal tibia was replaced to alleviate pain and restore function, but not the patella and corresponding trochlear groove. However, starting in the late 1970s, the use of bicruciate retaining baseplates started to decline as the introduction of the tricompartmental knees gained popularity and are not generally used in the current day knee joint replacement.
There is a never ending quest to improve/restore natural knee kinematics following total knee replacement especially with the baby boomer generation getting surgery at a much younger age and still expecting a return to normal, active lifestyle activities such as golf, biking, hiking, skiing. However, modern day implants still have limitations in offering natural joint kinematics. For example, a common misnomer in what the surgical community presently refers to as a Cruciate Retaining (CR) knee, the PCL is preserved but not the ACL. Therefore, the best that this knee can ever be is equivalent to an ACL deficient knee. In a Posterior Stabilized (PS) knee, both cruciates are sacrificed and only a partial function of the PCL is restored through the use of a cam on the femoral component and a post on the tibial insert, well known and understood in the current art. Therefore, since knees with compromised or torn cruciates are intrinsically unstable, it is believed that preserving both cruciates would improve joint stability and function following Total Knee Arthroplasty.
Some drawbacks of prior art bicruciate retaining baseplate designs are avulsion (tearing away) of the tibial eminence, and less than optimal instrumentation making surgery more challenging. In all bicruciate retaining baseplates, the medial and lateral compartments are connected by an anterior bridge portion. The corresponding bone preparation for the bridged portion is made with a vertical cut anterior to the ACL insertion site and extends distally to intersect the resection plane thereby resulting in a 90° corner. In loaded conditions, the ACL is under increased tension thereby loading that corner and making it susceptible to avulsion of the eminence. This risk increases significantly if the corner is undercut during preparation thus creating a notch.